U.S. patent number 10,107,996 [Application Number 15/168,704] was granted by the patent office on 2018-10-23 for wide-angle projection optical system.
This patent grant is currently assigned to DELTA ELECTRONICS, INC.. The grantee listed for this patent is DELTA ELECTRONICS, INC.. Invention is credited to Lai Chang Lin.
United States Patent |
10,107,996 |
Lin |
October 23, 2018 |
Wide-angle projection optical system
Abstract
A wide-angle projection optical system includes, between an
object side and an image side, a first optical system including a
first lens group having an aperture stop and a second lens group
disposed behind the aperture stop, and a second optical system
including a Mangin mirror and a glass plate disposed between the
second lens group and the Mangin mirror. The first and second lens
groups have positive power. The first lens group provides optical
characteristics to match with a light coming from the object side.
The first and second lens groups are configured to form an
aberrated real image. The Mangin mirror is disposed closer to the
image side than others. The Mangin mirror includes a refracting
surface and a reflecting surface for refracting the light two times
and reflecting the light one time, thereby producing an enlarged
real image on a screen. Therefore, the image quality is
enhanced.
Inventors: |
Lin; Lai Chang (Taoyuan,
TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
DELTA ELECTRONICS, INC. |
Taoyuan |
N/A |
TW |
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Assignee: |
DELTA ELECTRONICS, INC.
(Taoyuan, TW)
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Family
ID: |
56924637 |
Appl.
No.: |
15/168,704 |
Filed: |
May 31, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20160274344 A1 |
Sep 22, 2016 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14167782 |
Jan 29, 2014 |
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Foreign Application Priority Data
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Dec 5, 2013 [TW] |
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102144713 A |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03B
21/28 (20130101); G02B 13/18 (20130101); G02B
27/0025 (20130101); G02B 13/16 (20130101); G02B
13/04 (20130101); G02B 13/22 (20130101); G02B
17/0856 (20130101) |
Current International
Class: |
G02B
17/08 (20060101); G02B 13/16 (20060101); G02B
13/04 (20060101); G02B 13/22 (20060101); G02B
27/00 (20060101); G03B 21/28 (20060101); G02B
13/18 (20060101) |
Field of
Search: |
;359/649-651 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1667445 |
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Sep 2005 |
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CN |
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102782554 |
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Nov 2012 |
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CN |
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2955673 |
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Jul 2011 |
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FR |
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2004258620 |
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Sep 2004 |
|
JP |
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2005292813 |
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Oct 2005 |
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JP |
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2007127703 |
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May 2007 |
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JP |
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2011033737 |
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Feb 2011 |
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JP |
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2013015853 |
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Jan 2013 |
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JP |
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Primary Examiner: Schwartz; Jordan
Attorney, Agent or Firm: Kirton McConkie Witt; Evan R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part application of U.S.
application Ser. No. 14/167,782 filed on Jan. 29, 2014, which
claims the benefit of priority of Taiwan Application No. 102144713
filed on Dec. 5, 2013, the entirety of which is hereby incorporated
by reference.
Claims
What is claimed is:
1. A wide-angle projection optical system between an object side
and an image side thereof comprising: a first optical system
comprising: a first lens group having positive power and comprising
an aperture stop proximal to the image side, wherein light is
converged toward the aperture stop; and a second lens group having
positive power, wherein the second lens group is disposed on the
image side of the aperture stop; and a second optical system
comprising: a Mangin mirror disposed on the image side of the first
lens group and the second lens group, wherein the first lens group
and the second lens group are configured to form an aberrated real
image in front of the Mangin mirror, and wherein the Mangin mirror
includes a refracting surface and a reflecting surface for
refracting the light two times and reflecting the light one time,
thereby producing an enlarged real image on a screen; and a glass
plate disposed between the second lens group and the Mangin mirror,
wherein the glass plate comprises a black aperture disposed on the
glass plate for filtering the lights reflected by the refracting
surface, wherein the first lens group, the second lens group and
the Mangin mirror have a common optical axis.
2. The wide-angle projection optical system according to claim 1,
wherein the glass plate is disposed at a location where the lights
reflected by the reflecting surface are most concentrated.
3. The wide-angle projection optical system according to claim 1,
wherein the radius of curvature of the refracting surface and the
radius of curvature of the reflecting surface are different.
4. The wide-angle projection optical system according to claim 3,
wherein the ratio of the absolute value of the radius of curvature
of the refracting surface minus the radius of curvature of the
reflecting surface to the absolute value of the radius of curvature
of the refracting surface plus the radius of curvature of the
reflecting surface is greater than 0.12.
5. The wide-angle projection optical system according to claim 1,
wherein the Mangin mirror is a concave Mangin mirror having
positive power.
6. The wide-angle projection optical system according to claim 5,
wherein the center of curvature of the Mangin mirror is disposed
between the object side and the image side.
7. The wide-angle projection optical system according to claim 5,
wherein the Mangin mirror is concave toward the object side.
8. The wide-angle projection optical system according to claim 1,
wherein the light is transmitted through the refracting surface of
the Mangin mirror, reflected by the reflecting surface, and further
transmitted through the refracting surface in a reverse
direction.
9. The wide-angle projection optical system according to claim 1,
wherein each lens of the first lens group is axially symmetric and
is either a spherical lens or an aspheric lens.
10. The wide-angle projection optical system according to claim 1,
wherein both surfaces of at least one lens of the second lens group
are aspheric.
11. The wide-angle projection optical system according to claim 10,
wherein each lens of the second lens group is axially
symmetric.
12. The wide-angle projection optical system according to claim 1,
wherein the first optical system and the second optical system are
configured to form the wide-angle projection optical system as a
telecentric wide-angle projection optical system.
13. The wide-angle projection optical system according to claim 1,
wherein the first optical system and the second optical system are
configured to form the wide-angle projection optical system as a
non-telecentric wide-angle projection optical system.
14. A wide-angle projection optical system, from an object side to
an image side, the wide-angle projection optical system comprising:
a first optical system comprising: a first lens group having
positive power and comprising an aperture stop located proximal to
the image side, wherein light is converged toward the aperture
stop; and a second lens group having positive power, wherein the
second lens group is disposed on the image side of the aperture
stop, and both surfaces of at least one lens of the second lens
group are aspheric; and a second optical system comprising: a
refracting and reflecting mirror with positive power, wherein the
first lens group and the second lens group are configured to form
an aberrated real image in front of the refracting and reflecting
mirror with positive power, and wherein the refracting and
reflecting mirror includes a refracting surface and a reflecting
surface for refracting the light two times and reflecting the light
one time, thereby producing an enlarged real image on a screen; and
a glass plate disposed between the second lens group and the
refracting and reflecting mirror, wherein the glass plate comprises
a black aperture disposed on the glass plate for filtering the
lights reflected by the refracting surface; wherein the first lens
group, the second lens group and the refracting and reflecting
mirror have a common optical axis.
15. The wide-angle projection optical system according to claim 14,
wherein the glass plate is disposed at a location where the lights
reflected by the reflecting surface are most concentrated.
16. The wide-angle projection optical system according to claim 14,
wherein the radius of curvature of the refracting surface and the
radius of curvature of the reflecting surface are different.
17. The wide-angle projection optical system according to claim 16,
wherein the ratio of the absolute value of the radius of curvature
of the refracting surface minus the radius of curvature of the
reflecting surface to the absolute value of the radius of curvature
of the refracting surface plus the radius of curvature of the
reflecting surface is greater than 0.12.
Description
TECHNICAL FIELD
The present disclosure relates to a projection optical system, and
more particularly to an ultra-short-throw or a wide-angle
projection optical system.
BACKGROUND
A wide-angle projection lens has a large field of view, or a short
effective focal length (EFL). In comparison with a conventional
projection lens, the projection display apparatus with a wide-angle
projection lens is capable of producing a certain sized image at a
shorter distance.
Recently, an integrated system of a projection display apparatus
and an interactive white board has become very useful tool in
classrooms, lecture rooms or conference rooms in order to provide
the interactive functions about education, demonstration or
entertainment. FIG. 1A is a schematic diagram illustrating an
integrated system of a projection display apparatus and an
interactive white board according to the prior art. As shown in
FIG. 1A, the projection display apparatus 10 is usually mounted
upside down over the white board 11. The conventional short-throw
projection display apparatus 10 is usually mounted at a distance of
about 1 meter away from the white board 11. As such, the lecturer
with average height becomes an obstacle to the light path of the
projection display apparatus 10 when writing on the white board 11.
In addition, the eyes of the lecturer have the potential danger of
being illuminated by the light from the projection display
apparatus 10.
For solving the above problems, as shown in FIG. 1B, the projection
display apparatus 10 needs to be mounted in the vicinity of the
white board 11. Since the projection distance is very short, the
projection display apparatus 10 should have a wide-angle projection
lens to provide a large full field angle .theta. or a very short
focal length. In a case that the projection display apparatus 10
with a wide-angle projection lens is mounted over the white board
11, the light flux needs to incident on the white board 11 at a
very steep angle, which incurs a large distortion in the image.
Moreover, the projection lens also needs to have a large offset to
avoid the light hitting on the main body of the projection display
apparatus, and avoid the body of reflecting mirror blocking the top
area of the white board. In other words, the wide-angle or
ultra-short projection lens is very critical for designing the
projection display apparatus.
U.S. Pat. No. 7,529,032 disclosed a wide-angle projection optical
system. Please refer to FIG. 1C, which is a schematic diagram
illustrating the configuration of a wide-angle projection optical
system according to the prior art. As shown in FIG. 1C, the design
uses two aspheric plastic lenses, one double concave negative lens
and a negative aspheric reflecting mirror. The total length of the
system is quite long. This makes it difficult to have a thin
projector system. In addition, the maximum field angle is on the
order of 55 degree, which still requires a fairly long projection
distance to produce an image that is large enough for practical
applications.
FIG. 1D is a schematic diagram illustrating the configuration of
another wide-angle projection optical system according to the prior
art. U.S. Pat. No. 7,048,388 disclosed a wide-angle projection lens
design as shown in FIG. 1D that incorporates a flat mirror and a
positive aspheric reflecting mirror. However, the optical
components of the wide-angle projection optical system have to be
tilted and decentered in arrangement for obtaining an undistorted
image with better image quality. Otherwise, optical components
having anamorphic polynomial free-form surfaces with different
magnifications in vertical direction and horizontal direction are
necessary to be used in the wide-angle projection optical system,
and the complication of assembling or manufacturing optical
components are increased.
There is a need of providing a wide-angle projection optical system
to obviate the drawbacks encountered from the prior art.
BRIEF SUMMARY
It is an aspect of the present invention to provide a wide-angle
projection optical system with short-throw in order to eliminate
the drawbacks of dangers of a conventional optical system,
distortions and aberrations.
An another aspect of the present invention provides a wide-angle
projection optical system with ultra-short-throw having a large
full field angle, which is for example larger than 70 degrees, a
short effective focal length, thin profile, low distortion and
aberration and high image quality.
An another aspect of the present invention provides a wide-angle
projection optical system with a second optical system comprising a
Mangin mirror and a glass plate. By the glass plate, a spatial
filtering can be implemented to remedy the ghost image. More
specifically, if the radius of curvatures of the refracting surface
and the reflecting surface are sufficiently different, the light
distributions of the lights reflected by the reflecting surface and
the lights reflected by the refracting surface will be
well-separated.
In accordance with an aspect of the present disclosure, there is
provided a wide-angle projection optical system. The wide-angle
projection optical system includes, between an object side and an
image side, a first optical system including a first lens group
having an aperture stop therein and a second lens group, and a
second optical system including a Mangin mirror and a glass plate.
The first lens group has positive power, and the second lens group
has positive power. The aperture stop is located on the most image
side of the first lens group. The first lens group provides optical
characteristics to match with a light coming from the object side.
The light is converged toward the aperture stop. The second lens
group is disposed on the image side of (i.e. behind) the aperture
stop. The first lens group and the second lens group are configured
to form an aberrated real image in front of the Mangin mirror. The
Mangin mirror is disposed closer to the image side than the first
lens group, the aperture stop and the second lens group. The Mangin
mirror includes a refracting surface and a reflecting surface for
refracting the light two times and reflecting the light one time,
thereby producing an enlarged real image on a screen. The glass
plate is disposed between the second lens group and the Mangin
mirror.
In accordance with another aspect of the present disclosure, there
is provided a wide-angle projection optical system. The wide-angle
projection optical system includes, from an object side to an image
side, a first optical system including a first lens group having an
aperture stop therein and a second lens group, and a second optical
system including a refracting and reflecting mirror with positive
power and a glass plate. The first lens group has positive power,
and the second lens group has positive power. The aperture stop is
located on the most image side of the first lens group. The first
lens group provides optical characteristics to match with a light
coming from the object side. The light is converged toward the
aperture stop. The second lens group is disposed on the image side
of (i.e. behind) the aperture stop, and both surfaces of at least
one lens of the second lens group are aspheric. The first lens
group and the second lens group are configured to form an aberrated
real image in front of the refracting and reflecting mirror with
positive power. The refracting and reflecting mirror includes a
refracting surface and a reflecting surface for refracting the
light two times and reflecting the light one time, thereby
producing an enlarged real image on a screen. The glass plate is
disposed between the second lens group and the refracting and
reflecting mirror. The first lens group, the second lens group and
the refracting and reflecting mirror have a common optical
axis.
The above contents of the present disclosure will become more
readily apparent to those ordinarily skilled in the art after
reviewing the following detailed description and accompanying
drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematic diagram illustrating an integrated system of
a projection display apparatus and an interactive white board
according to the prior art;
FIG. 1B is a schematic diagram illustrating an integrated system of
a wide-angle projection display apparatus and an interactive white
board according to the prior art;
FIG. 1C is a schematic diagram illustrating the configuration of a
wide-angle projection optical system according to the prior
art;
FIG. 1D is a schematic diagram illustrating the configuration of
another wide-angle projection optical system according to the prior
art;
FIG. 2 is a schematic diagram illustrating the configuration of a
wide-angle projection optical system according to an embodiment of
the present invention;
FIG. 3 is a schematic diagram illustrating the detailed structure
of a Mangin mirror of the wide-angle projection optical system
according to an embodiment of the present invention;
FIG. 4 is a schematic diagram illustrating modulation transfer
function (MTF) characteristics in the image side by the wide-angle
projection optical system according to the embodiment of the
present invention with the values shown in Table 1;
FIG. 5A is a schematic diagram illustrating grid distortion in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 1;
FIG. 5B is a schematic diagram illustrating distortion curve in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 1;
FIG. 6 is a schematic diagram illustrating lateral color in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 1;
FIG. 7 is a schematic diagram illustrating the light reflected by
the refracting surface due to Fresnel reflection and the light
reflected by the reflecting surface of a Mangin mirror of the
wide-angle projection optical system according to an embodiment of
the present invention;
FIG. 8 is a schematic diagram illustrating the detailed
configuration of the second optical system comprising a glass plate
according to an embodiment of the present invention;
FIG. 9A is a schematic diagram illustrating a light distribution
diagram of the lights reflected by the reflecting surface of the
Mangin mirror;
FIG. 9B is a schematic diagram illustrating a light distribution
diagram of the lights reflected by the refracting surface of the
Mangin mirror due to Fresnel reflection;
FIG. 10 is a schematic diagram illustrating a light distribution
diagram of the lights reflected by the reflecting surface of the
Mangin mirror and the light filtered by a black aperture placed on
the glass plate of the second optical system;
FIG. 11 is a schematic diagram illustrating the configuration of a
wide-angle projection optical system according to another
embodiment of the present invention;
FIG. 12 is a schematic diagram illustrating modulation transfer
function (MTF) characteristics in the image side by the wide-angle
projection optical system according to the embodiment of the
present invention with the values shown in Table 3;
FIG. 13A is a schematic diagram illustrating grid distortion in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 3;
FIG. 13B is a schematic diagram illustrating distortion curve in
the image side by the wide-angle projection optical system
according to the embodiment of the present invention with the
values shown in Table 3; and
FIG. 14 is a schematic diagram illustrating lateral color in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present disclosure will now be described more specifically with
reference to the following embodiments. It is to be noted that the
following descriptions of preferred embodiments of this disclosure
are presented herein for purpose of illustration and description
only. It is not intended to be exhaustive or to be limited to the
precise form disclosed.
Please refer to FIG. 2. FIG. 2 is a schematic diagram illustrating
the configuration of a wide-angle projection optical system
according to an embodiment of the present invention. As shown in
FIG. 2, the wide-angle projection optical system 2 is a
non-telecentric projection optical system, which can be applied to
a projection display apparatus. The projection display apparatus
includes, but not limited to, a digital micromirror device
(hereinafter "DMD"). The DMD has an object surface 3, which is an
image-displaying surface of a light valve. The object surface 3 is
configured as an object side A for the image projected by the
wide-angle projection optical system 2 of the present invention to
be formed on. In this embodiment, the wide-angle projection optical
system 2 includes, between the object side A and an image side B, a
first optical system 21 and a second optical system 22, among which
the first optical system 21 and the second optical system 22 are
configured to form the wide-angle projection optical system 2 as a
non-telecentric wide-angle projection optical system. The first
optical system 21 includes a first lens group 211 having positive
power and including a aperture stop 212 and a second lens group 213
having positive power, and the second optical system 22 includes a
Mangin mirror 221. The first lens group 211 sets up proper working
space and pupil position to match with optical characteristics of a
light coming from an illumination optical system (i.e. the object
side). In other words, the first lens group 211 is configured to
provide optical characteristics to match with a light coming from
the object side A and converge the light toward the aperture stop
212, such that the light is further projected or outputted to the
second lens group 213.
In particular, the first lens group 211 of the wide-angle
projection optical system 2 consists of a plurality of refraction
lenses and has positive effective optical power for providing the
telecentricity of object space and converging the light emitted
toward the aperture stop 212 by the DMD. In this embodiment, the
aperture stop 212 is located in the first lens group 211 and at the
focus point of the main light. Moreover, the Mangin mirror 221 is
disposed closer to the image side B than the first lens group 211,
the aperture stop 212 and the second lens group 213. An aberrated
real image is formed by the first lens group 211 and the second
lens group 213. The Mangin mirror 221 includes a refracting surface
2211 and a reflecting surface 2212 for refracting the light two
times and reflecting the light one time, thereby producing an
enlarged real image on a screen in order to correct aberration and
distortion. Therefore, the full field angle is enhanced, and the
projection lens or the body of the projection display apparatus can
be located between the reflecting mirror and the screen, thereby
miniaturizing the integrated projection system.
In some embodiments, the Mangin mirror 221 is a concave Mangin
mirror having positive power, and the center of curvature of the
Mangin mirror is disposed between the object side A and the image
side B.
The first lens group 211, the aperture stop 212 and the second lens
group 213 of the first optical system 21 and the Mangin mirror 221
of the second optical system 22 of the wide-angle projection
optical system 2 of one embodiment of the present invention are
arranged sequentially from the object side A to the image side B,
but are not limited thereto. Every lens of the first lens group 211
and the second lens group 213 and the Mangin mirror 221 have a
common optical axis. In addition, the exteriors of each lens of the
first lens group 211 and each lens of the second lens group 213 of
the first optical system 21 and the Mangin mirror 221 of the second
optical system 22 are axially symmetric relative to the common
optical axis.
In this embodiment, the surfaces of each lens of the first lens
group 211 are spherical, but aspheric surfaces also can be used to
further reduce the aberration and distortion of the final image in
other embodiments. That is, both surfaces of each lens of the first
lens group 211 (e.g. the front surface and the rear surface) are
either spherical or aspheric. Furthermore, at least one lens of the
second lens group 213 is an aspheric lens. Both surfaces, namely
the front surface and the rear surface, of at least one lens of the
second lens group 213 are aspheric in order to correct aberration
and distortion. In each embodiment of the present invention, the
effective optical power is properly distributed among the lenses of
the first lens group 211 and/or the second lens group 213 in order
to lower the sensitivity to mechanical tolerances.
Please refer to FIG. 2 and FIG. 3. FIG. 3 is a schematic diagram
illustrating the detailed structure of a Mangin mirror of the
wide-angle projection optical system according to an embodiment of
the present invention. As shown in FIG. 2 and FIG. 3, the Mangin
mirror 221 of the second optical system 22 of the wide-angle
projection optical system 2 has positive power, and the Mangin
mirror is preferably a refracting and reflecting mirror and not
limited to a meniscus lens coated with an anti-reflecting coating
(ARC). In some preferable embodiments, the light I projected or
emitted through the object side A, the first lens group 211, the
aperture stop 212 and the second lens group 213 is transmitted
through the refracting surface 2211 of the Mangin mirror 221 from
the air, reflected by the reflecting surface 2212, and further
transmitted through the refracting surface 2211 in a reverse
direction, so the two refractions and the one reflection are
implemented. In brief, regarding the optical path of the two
refractions and the one reflection of the light I, it can be
considered as transmitting through three mediums. Compared with the
conventional reflecting mirror applied in the prior art, the design
factor and design parameter are added in the present invention, so
that the optical system can be easily designed and adjusted for
reducing the image distortion and the image aberration. Moreover,
by utilizing the refracting surface 2211 and the reflecting surface
2212 of the Mangin mirror 221, the anamorphic polynomial free-form
surfaces are not necessary in design of the wide-angle projection
optical system 2 of the present disclosure. That is, none of any
non-axially symmetric optical component is used in the present
invention, so that the manufacturing difficulty is reduced, and
tight tolerances are avoided.
Table 1 shows the prescription data of the lenses. In Table 1,
"No." is a surface number from the object side to the image side.
"R" indicates radius of curvature, "T" indicates the thickness,
"Nd" indicates a refractive index, and "Vd" indicates an Abbe
number. The front and rear surfaces of the lenses No. 13, No. 14,
No. 19, No. 20, No. 21, and No. 22 are all aspheric. The aspheric
coefficients (k, A4, A6, A8, A10 and A12) of these surfaces are
listed in Table 2. As a consequence, wide-angle projection optical
system 2 of the present invention can achieve a full field angle
larger than .+-.70 degrees. In this embodiment the micro-display is
illuminated by a non-telecentric illumination system. This means
that the central rays from each filed on the micro-display are
essentially concentrated toward a point at a finite distance from
the micro-display. The surface figure of the aspheric surface is
described by the following equation.
.function..times..times..times..times..times..times..times..times.
##EQU00001##
In this equation, Z(r) indicates the bending amount (sag) of a
surface, C=1/R, and r indicates the distance between a surface and
the optical axis.
TABLE-US-00001 TABLE 1 No. R T Nd Vd 0 Infinity 0.7 1 Infinity
1.050 1.51 63.0 2 Infinity 19.936 3 -1421.486 2.614 1.50 81.5 4
-29.764 0.15 5 410.168 2.306 1.60 65.4 6 -47.968 2.954 7 -20.458
1.000 1.67 33.0 8 21.148 3.286 1.5 81.5 9 -29.890 0.960 10 Infinity
0.361 11 42.326 2.935 1.67 48.3 12 -31.694 23.320 13 72.172 6.589
1.53 56.0 14 -1692.620 1.439 15 56.672 5.066 1.65 39.7 16 -138.685
3.492 17 -33.126 6.706 1.60 65.4 18 196.555 1.561 19 -89.079 4.505
1.53 56 20 32.955 103.683 21 -86.710 6.923 1.53 56 22 -62.982
-6.923 -1 0 23 -86.710 -613.116 24 Infinity
TABLE-US-00002 TABLE 2 No. k A4 A6 A8 A10 A12 13 -8.826 -1.334e-5
-2.443e-8 -5.594e-11 -3.515e-13 3.856e-16 14 3.09e+05 4.526e-6
2.188e-8 -7.790e-11 1.208e-14 1.016e-15 19 -50.607 8.271e-6
9.983e-9 3.272e-11 -6.168e-13 1.723e-17 20 -4.391 -3.152e-6
2.616e-9 2.269e-12 8.648e-15 5.275e-18 21 -1.877 -8.721e-7
2.383e-11 9.764e-15 -1.020e-18 2.334e-23 22 -2.965 -8.610e-7
5.423e-11 -5.071e-16 -3.133e-19 5.454e-24 23 -1.877 -8.721e-7
2.383e-11 9.764e-15 -1.020e-18 2.334e-23
FIG. 4 is a schematic diagram illustrating modulation transfer
function (MTF) characteristics in the image side by the wide-angle
projection optical system according to the embodiment of the
present invention with the values shown in Table 1. The horizontal
axis indicates spatial frequency (cycles/mm) and the vertical axis
of ordinates indicates modulation values. The spatial frequency
indicates the number of sine waves per millimeter. The maximum
value 1 in the vertical axis indicates that the MTF is 100%. As
shown in FIG. 4, in the Nyquist Frequency, the MTF is still greater
than 50%, which means the MTF ratio does not obviously decrease, so
that every pixel is clearly resolved in achieving high quality
image. FIG. 5A is a schematic diagram illustrating grid distortion
in the image side by the wide-angle projection optical system
according to the embodiment of the present invention with the
values shown in Table 1. FIG. 5B is a schematic diagram
illustrating distortion curve in the image side by the wide-angle
projection optical system according to the embodiment of the
present invention with the values shown in Table 1. As shown in
FIG. 5A and FIG. 5B, the grid distortion or image distortion can be
effectively corrected in the projection areas of the embodiment.
FIG. 6 is a schematic diagram illustrating lateral color in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 1. As shown in FIG. 6, the difference of the lateral colors
is less than a pixel, so that the color dislocation issue is
avoided when projecting color lights, which means the chromatic
aberration is also effectively corrected by the present invention.
From the above drawings, the wide-angle projection optical system 2
of the present invention has a large full field angle, low image
aberration or distortion, good optical characteristics and high
image quality. A projection with high image quality and low image
distortion is implemented by the embodiments mentioned above
without any non-axially symmetric optical component.
In some embodiments, there is one negative aspect of using Mangin
mirror. Please refer to FIG. 7. FIG. 7 is a schematic diagram
illustrating the light reflected by the refracting surface due to
Fresnel reflection and the light reflected by the reflecting
surface of a Mangin mirror of the wide-angle projection optical
system according to an embodiment of the present invention. When
refracting at the refracting surface 2211 of the Mangin mirror 221,
a small amount of the light I will be reflected as the extraneous
light G by the refracting surface 2211 due to Fresnel reflection,
even though the refracting surface 2211 is usually anti-reflection
coated. The extraneous light G is shown as dotted line in FIG. 7.
The extraneous light G will travel at angles close to the light N
reflected by the reflecting surface 2212 and form a defocused image
on the screen. This type of artifact is usually called "ghost
image".
One way to remedy the ghost image is spatial filtering. Please
refer to FIG. 2 and FIGS. 8-10. FIG. 8 is a schematic diagram
illustrating the detailed configuration of the second optical
system comprising a glass plate according to an embodiment of the
present invention. FIG. 9A is a schematic diagram illustrating a
light distribution diagram of the lights reflected by the
reflecting surface of the Mangin mirror. FIG. 9B is a schematic
diagram illustrating a light distribution diagram of the lights
reflected by the refracting surface of the Mangin mirror due to
Fresnel reflection. FIG. 10 is a schematic diagram illustrating a
light distribution diagram of the lights reflected by the
reflecting surface of the Mangin mirror and the light filtered by a
black aperture placed on the glass plate of the second optical
system.
As shown in FIG. 2 and FIG. 8, the second optical system 22 further
comprises a glass plate 222. The glass plate 222 is disposed
between the second lens group 213 and the Mangin mirror 221, and
particularly at a location where the lights reflected by the
reflecting surface 2212 are most concentrated. If the radius of
curvatures of the refracting surface 2211 and the reflecting
surface 2212 are sufficiently different, the light distributions of
the lights reflected by the reflecting surface 2212 and the lights
reflected by the refracting surface 2211 (i.e. the extraneous
lights) will be well-separated. A black aperture 2221 can be
disposed on the glass plate 222 to filter out the extraneous lights
and thus eliminate the ghost image as shown in FIG. 10.
As mentioned above, in order for the spatial filtering technique to
be effective in eliminating ghost image, the radius of curvatures
of the refracting surface 2211 and the reflecting surface 2212 need
to be sufficiently different. It is preferable that the curvatures
meet the following condition: Absolute value of (R1-R2)/Absolute
value of (R1+R2)>0.12, which can be written by
|R1-R2|/|R1+R2|>0.12, in which R1 is the radius of curvature of
the refracting surface 2211 and R2 is the radius of curvature of
the reflecting surface 2212 of the Mangin mirror 221.
Please refer to FIG. 11. FIG. 11 is a schematic diagram
illustrating the configuration of a wide-angle projection optical
system according to another embodiment of the present invention. As
shown in FIG. 11, an object surface 3 is configured as an object
side A for the image projected by the wide-angle projection optical
system 4 of the present invention to be formed on. In this
embodiment, the wide-angle projection optical system 4 includes,
sequentially arranged from the object side A to an image side B, a
first optical system 41 and a second optical system 42, and the
first optical system 41 and the second optical system 42 are
configured to form the wide-angle projection optical system 4 as a
telecentric wide-angle projection optical system. The first optical
system 41 includes a first lens group 411 having positive power and
including a aperture stop 412 and a second lens group 413 having
positive power, and the second optical system 42 includes a
refracting and reflecting mirror 421. The first lens group 411, the
aperture stop 412, the second lens group 413 and the refracting and
reflecting mirror 421 are similar with the first lens group 211,
the aperture stop 212, the second lens group 213 and the Mangin
mirror 221 of the above-mentioned embodiment, and not redundantly
described herein. It should be noted that the wide-angle projection
optical system of the present invention can be a non-telecentric
wide-angle projection optical system or a telecentric wide-angle
projection optical system for being utilized in digital light
processing (DLP) device or liquid crystal displaying (LCD)
device.
Table 3 shows the prescription data of the lenses according to this
embodiment. In Table 3, "No." is a surface number from the object
side to the image side. "R" indicates radius of curvature, "T"
indicates the thickness, "Nd" indicates a refractive index, and
"Vd" indicates an Abbe number. The front and rear surfaces of the
lenses No. 18, No. 19, No. 24, No. 25, No. 26, NO. 27 and No. 28
are all aspheric. The aspheric coefficients (k, A4, A6, A8, A10 and
A12) of these surfaces are listed in Table 4. As a consequence,
wide-angle projection optical system 2 of the present invention can
achieve a full field angle larger than .+-.70 degrees. In this
embodiment the micro-display is illuminated by a telecentric
illumination system. This means that the central rays from each
filed on the micro-display are essentially collimated from the
micro-display.
TABLE-US-00003 TABLE 3 No. R T Nd Vd 0 Infinity 0.7 1 Infinity
1.050 1.51 63.0 2 Infinity 1 3 Infinity 18 1.52 64.1 4 Infinity 5 5
48.9351 5.448 1.50 81.5 6 -69.6432 0.128 7 350.5973 3.62 1.49 70.2
8 -60.8138 0.15 9 53.6141 4.219 1.50 81.5 10 -91.3327 1.86 11
85.8327 11.213 1.75 35.3 12 75.3116 3.026 13 -20.8099 2.834 1.69
31.1 14 18.2072 4.347 1.50 81.5 15 -33.3142 1.848 16 36.1211 11.073
1.60 39.2 17 -37.1867 20.315 18 49.3392 5.21 1.53 56.0 19
-5321.1473 0.196 20 69.0805 5.819 1.76 27.5 21 -337.8203 3.626 22
-32.3685 11 1.62 60.3 23 743.4352 1.637 24 -43.9674 5.485 1.53 56.0
25 34.7057 102.68 26 -82.1935 6.244 1.53 56.0 27 -62.4958 -6.244 -1
0 28 -82.1935 -625.847 29 Infinity
TABLE-US-00004 TABLE 4 No. k A4 A6 A8 A10 A12 18 0.0352 -7.1386e-6
-8.1380e-9 -5.3639e-11 -3.4127e-13 -5.6496e-16 19 -932.1597
1.2229e-6 5.0426e-9 -7.9514e-11 -3.0201e-13 2.9009e-16 24 -11.1474
1.0568e-5 1.6169e-8 3.9028e-11 -8.8211e-14 1.9858e-17 25 -4.7449
-2.0330e-6 6.3947e-9 5.6832e-12 4.6915e-15 1.0894e-17 26 -1.9369
-8.7074e-7 2.3081e-11 9.7287e-15 1.0514e-18 2.0919e-23 27 -2.8101
-8.5863e-7 5.3320e-11 -7.9959e-16 -3.2209e-19 5.7242e-24 28 -1.9369
-8.5863e-7 5.3320e-11 -7.9959e-16 -3.2209e-19 5.7242e-24
FIG. 12 is a schematic diagram illustrating modulation transfer
function (MTF) characteristics in the image side by the wide-angle
projection optical system according to the embodiment of the
present invention with the values shown in Table 3. The horizontal
axis indicates spatial frequency (cycles/mm) and the vertical axis
of ordinates indicates modulation values. The spatial frequency
indicates the number of sine waves per millimeter. The maximum
value 1 in the vertical axis indicates that the MTF is 100%. As
shown in FIG. 4, in the Nyquist Frequency, the MTF is still greater
than 50%, which means the MTF ratio does not obviously decrease, so
that every pixel is clearly resolved in achieving high quality
image. FIG. 13A is a schematic diagram illustrating grid distortion
in the image side by the wide-angle projection optical system
according to the embodiment of the present invention with the
values shown in Table 3. FIG. 13B is a schematic diagram
illustrating distortion curve in the image side by the wide-angle
projection optical system according to the embodiment of the
present invention with the values shown in Table 3. As shown in
FIG. 5A and FIG. 5B, the grid distortion or image distortion can be
effectively corrected in the projection areas of the embodiment.
FIG. 14 is a schematic diagram illustrating lateral color in the
image side by the wide-angle projection optical system according to
the embodiment of the present invention with the values shown in
Table 3. As shown in FIG. 6, the difference of the lateral colors
is less than a pixel, so that the color dislocation issue is
avoided when projecting color lights, which means the chromatic
aberration is also effectively corrected by the present invention.
From the above drawings, the wide-angle projection optical system 2
of the present invention has a large full field angle, low image
aberration or distortion, good optical characteristics and high
image quality. A projection with high image quality and low image
distortion is implemented by the embodiments mentioned above
without any non-axially symmetric optical component.
From the above description, the wide-angle projection optical
system with ultra-short-throw of the present invention is capable
of providing a large full field angle. The wide-angle projection
optical system comprises a first lens group with positive power, a
second lens group with positive power, and a Mangin mirror having a
refracting surface and a reflecting surface. The wide-angle
projection optical system may provide a full field angle larger
than .+-.70 degrees, a very short effective focal length, low image
distortion and high image quality. The use of the wide-angle
projection optical system makes the compact and thin display system
possible. Moreover, by means of the wide-angle projection optical
system, the projection display apparatus may be installed over the
white board or the display screen.
While the disclosure has been described in terms of what is
presently considered to be the most practical and preferred
embodiments, it is to be understood that the disclosure needs not
be limited to the disclosed embodiment. On the contrary, it is
intended to cover various modifications and similar arrangements
included within the spirit and scope of the appended claims, which
are to be accorded with the broadest interpretation so as to
encompass all such modifications and similar structures.
* * * * *